EP0362775A1 - Dispositif de décompression pour moteur à combustion interne - Google Patents

Dispositif de décompression pour moteur à combustion interne Download PDF

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Publication number
EP0362775A1
EP0362775A1 EP89118252A EP89118252A EP0362775A1 EP 0362775 A1 EP0362775 A1 EP 0362775A1 EP 89118252 A EP89118252 A EP 89118252A EP 89118252 A EP89118252 A EP 89118252A EP 0362775 A1 EP0362775 A1 EP 0362775A1
Authority
EP
European Patent Office
Prior art keywords
cam
pivot shaft
release lever
decompression
driven gear
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP89118252A
Other languages
German (de)
English (en)
Inventor
Katsuhiko C/O Fuji Jukogyo K.K. Ohno
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Subaru Corp
Original Assignee
Fuji Jukogyo KK
Fuji Heavy Industries Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fuji Jukogyo KK, Fuji Heavy Industries Ltd filed Critical Fuji Jukogyo KK
Publication of EP0362775A1 publication Critical patent/EP0362775A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
    • F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
    • F01L13/08—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for decompression, e.g. during starting; for changing compression ratio
    • F01L13/085—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for decompression, e.g. during starting; for changing compression ratio the valve-gear having an auxiliary cam protruding from the main cam profile
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B2275/00—Other engines, components or details, not provided for in other groups of this subclass
    • F02B2275/22—Side valves

Definitions

  • the present invention relates generally to internal combustion engines and decompression devices thereof. More particularly, the invention concerns a decompression device of an engine of high compression ratio which device, at the time of starting of the engine, forcibly opens at least one of the valves of each cylinder thereby to provide easy starting.
  • decompression devices have heretofore been proposed to facilitate such manual starting.
  • at least one of the intake valves or the exhaust valves is forcibly opened to a partial degree, as disclosed in Japanese Utility Model Laid-Open (Unexamined) Publication No. 97308/1985.
  • a decompression device of this type essentially has the following construction.
  • a release lever is fixed at its proximal end to a pivot pin.
  • the pivot pin is rotatably supported on a cam driven gear.
  • An end of the release lever constitutes a flyweight.
  • a return spring is provided at its one end to a pin fixed to the cam driven gear and at the other end to the end of the release lever.
  • a decompression cam is formed at an end part of the pivot pin mentioned above. The decompression cam is in contact with a tappet of a valve of the engine.
  • the return spring is retaining the release lever at a "closed" angular position.
  • the decompression cam is raising the tappet to a position outside the base circle or minimum radius of the corresponding cam.
  • the corresponding valve is therefore in a partially opened state. Decompression is thus obtained.
  • This decompression device of the prior art which will be described in detail hereinafter, is accompanied by certain problems arising primarily from the nature of the return spring.
  • One problem is the lack of space for satisfactory decompression operation of the mechanism.
  • Another problem is the vulnerability of the return spring to adverse causes such as vibration.
  • the present invention has been made in view of the above described circumstances of the prior art. It is an object of the present invention to provide an engine decompression device which is of simple construction and has the following features.
  • the return spring does not strike or interfere with other constituent parts even in a small space.
  • the device cam perform decompression positively. Furthermore, the device is not easily affected adversely by external disturbances such as vibration.
  • a decompression device of an engine having a camshaft, a cam driven gear fixed to the camshaft and driven by the crankshaft of the engine, a valve cam fixed to the camshaft, a tappet actuated by the valve cam to open and close a valve of a cylinder of the engine, and a release lever pivotally supported on the cam driven gear thereby to be swingable in opening and closing directions in a plane parallel to the cam driven gear and being urged by centrifugal force to swing in an opening direction; said compression device comprising a pivot shaft fixed perpendicularly to the release lever and rotatably fitted in the cam driven gear thereby to pivotally support the release lever; and a coil spring fitted loosely around the pivot shaft and anchored at one end to the pivot shaft and at the other end to the cam driven gear thereby to exert a return torque on the release lever urging the same to rotate in a closing direction, the pivot shaft having a decompression cam which is shaped such that during a compression stroke and when the
  • a longitudinal cutout surface is provided in the camshaft, and the decompression cam is disposed close to the cutout surface of the camshaft and partially within the base circle of the valve cam and comprises a flat part of the pivot shaft formed parallel to the pivot shaft axis as a longitudinal cutout surface of the pivot shaft at the end thereof remote from the release lever, the longitudinally inner end of the flat surface and an intermediate part of the pivot shaft being joined by way of a tapered part to form a continuous surface, the flat surface confronting the tappet when the release lever swings in the opening direction, the end part of the pivot shaft other than the flat surface contacting the tappet thereby to move the tappet to a position for partially opening the valve when the release lever is returned in the closing direction.
  • the pivot shaft of the release lever is first inserted into and rotatably supported on the cam driven gear. Thereafter the coil torsion spring is fitted around the decompression cam part formed at the end of the pivot shaft so that the end of the spring to be anchored to the pivot shaft is remote from the release lever.
  • the other end of the coil spring is anchored to the cam driven gear.
  • the coil spring thus exerts constantly a torque on the release lever tending to rotate it in its closing direction. Consequently the decompression cam, pushing the tappet, forcibly opens the valve.
  • the initial rotational speed of the engine at the time of starting is low. Therefore, the centrifugal force acting on the release lever is insufficient to overcome the returning force of the coil spring.
  • the decompression cam thereby forcibly opens the valve. Thus the combustion chamber of the cylinder is decompressed.
  • An essential part of the conventional decompression device shown in FIG. 6 is a release lever 2 pivotally supported at a pivot pin part 2a thereof on a cam driven gear 5.
  • the cam driven gear 5 is meshed with a cam drive gear (not shown) unitarily fixed to the crankshaft (also not shown) of an engine.
  • the cam driven gear 5 is fixed to the camshaft 1.
  • a return spring 3 in stretched state is anchored at its one end to a pin 5a fixed to the cam driven gear 5 and is connected at its other end to the distal end of the release lever 2.
  • the release lever 2 is thus urged by the return spring 3 to rotate about its pivot pin part 2a in the counterclockwise direction as viewed in FIG. 6.
  • a decompression cam 2b is formed at an end part of the pivot pin part 2a.
  • the decompression cam 2b is in contact with a valve tappet 4.
  • the decompression cam 2b functions upon rotating to lift the tappet 4 forcibly to a highest position as indicated by single-dot chain lines.
  • the pressure within the cylinder combustion chamber 21 (FIG. 1) is thus lowered slightly.
  • the release lever 2 mentioned above has a shape such that a flyweight 2c is formed at its distal end remote from its pivot pin part 2a. After the engine has been started, its speed increases. Therefore the centrifugal force acting on the flyweight 2c gradually increases. Consequently the release lever 2 is urged by the centrifugal force to move in the direction counter to that of the force of the return spring 3. As a result, the decompression cam 2b is turned to an angle at which its effective cam surface is accommodated within the base circle, or minimum radius of the corresponding cam 1a provided on the camshaft 1. Therefore the decompression is automatically ended.
  • the decompression device of the prior art is accompanied by the following problems.
  • the diameter of the cam driven gear 5 must be determined so as to obtain an ample space for assuring stretching of the return spring 3.
  • the engine with the decompression device according to the present invention is applied is a conventional vertical-shaft engine E shown in FIG. 1.
  • the engine has an oil pan 11 formed integrally with the engine crankcase 22.
  • a pump housing 12 is formed as shown in FIG. 2.
  • An oil pump (trochoid pump) 13 is housed within the pump housing 12.
  • a camshaft bearing 14 is fitted into and fixed to the pump housing 12.
  • a journal 15a formed at the lower end of the camshaft 15 is rotatably supported by the bearing 14.
  • a flange-like stepped part 15b is formed on the camshaft 15.
  • the annular lower surface of the stepped part 15b rests rotatably on the upper end of the camshaft bearing 14 over a thrust shim 16 interposed therebetween.
  • An oil passage 15c is formed centrally in the camshaft 15.
  • the oil pump 13 has a driving shaft 13a coupled to the camshaft 15 at a lower end opening of the oil passage 15c.
  • a cam driven gear 15d is formed coaxially with the camshaft 15.
  • the cam driven gear 15d is meshed with a cam drive gear coaxially fixed to the engine crankshaft 20 (FIG. 1).
  • an exhaust cam 15e is formed integrally with the camshaft 15. The cam surface of the exhaust cam 15e is slidably contacted by an exhaust tappet 17 connected to the exhaust valve (not shown).
  • a journal part of the upper end of the camshaft 15 is rotatably supported by a bearing provided at an upper part of the engine crankcase 22.
  • a flat cutout 15f is formed on one lateral side of the camshaft 15 at a part thereof below the lower surface of the exhaust cam 15e and facing the exhaust tappet 17 at the time of the compression stroke. That is, the cutout 15f is positioned on the back side of the cam lobe of the exhaust cam 15e.
  • the cutout 15f is confronted by a decompression cam 18b formed at the upper end part of a pivot shaft 18a of a release lever 18.
  • the pivot shaft 18a extends through and is rotatably supported in a bore 15g formed in the cam driven gear 15d.
  • the lower base end of the pivot shaft 18a is seated on the thrust shim 16 mentioned before.
  • the release lever 18 has a curved claw-like shape as viewed in plan view in FIG.3 and is fixed at its proximal end on the lower base end of the pivot shaft 18a.
  • the release lever 18 is disposed below and parallel to the lower surface of the cam driven gear 15d.
  • the release lever 18 is thereby pivotable about the axis of the pivot shaft 18a.
  • the outer part of the release lever 18 constitutes a flyweight 18c.
  • a centrifugal force acts on the flyweight 18c.
  • the flyweight is thereby urged to swing outwardly in an "opening" direction about the axis of the pivot shaft 18a. This swinging direction is counterclockwise as viewed in FIG. 3.
  • the angle of this swing of the release lever 18 is limited by a stop pin 19 imbeddedly fixed to the lower surface of the cam driven gear 15d.
  • the pivot shaft 18a at the upper end has a lift part 18d in addition to the aforementioned decompression cam 18b. Furthermore, a flat part 18e of the decompression cam 18b is formed as a flat cutout in the upper part of the pivot shaft 18a. Contiguous to the lower end of the flat part 18e is formed a tapered part 18f. A transverse hole 18g is formed through the pivot shaft 18a at a position below the lower end of the tapered part 18f.
  • a coil spring 20 is loosely fitted around the upper part of the pivot shaft 18a below the tapered part 18f thereof.
  • the upper end of the coil spring 20 is bent inwardly to form an anchor part 20a.
  • the anchor part 20a is fitted in and engaged with the hole 18g in the pivot shaft 18a.
  • the other end of the coil spring 20 extends away from the pivot shaft 18a.
  • An end of the spring 20 is formed into a hook 20b (FIG. 2).
  • the hook 20b is engaged with the upper end of a vertical stud pin 21 press fitted into the cam driven gear 15d.
  • the coil spring 20 applies a certain torque to the release lever 18 urging it to rotate in the "closing" direction, i.e., clockwise as viewed in FIG. 3.
  • the release lever 18 and therefore the flyweight 18c
  • the lift part 18d of the decompression cam 18b formed at the upper end of the pivot shaft 18a is projected outside of the base circle of the exhaust cam 15e.
  • the decompression device of the above described construction according to the present invention is assembled in the following manner.
  • the coil spring 20 is placed in the cutout 15f formed in the camshaft 15. Then the pivot shaft 18a of the release lever 18, which has been previously assembled in a prescribed manner, is inserted upwardly through the bore 15g from below the cam driven gear 15d.
  • the decompression cam 18b provided at the upper tip of the pivot shaft 18a is thereupon inserted through the coil spring 20 placed in the cutout 15f. Then the pivot shaft 18a is inserted further upwardly.
  • the anchor part 20a formed at the upper end of the coil spring 20 is thereupon guided in sliding movement along and relative to the tapered part 18f contiguous to the flat part 18e of the decompression cam 18b.
  • the anchor part 20a is thus forced to open outwardly until the tip reaches the hole 18g formed in the back of the tapered part 18f.
  • the anchor part 20a is thereupon forced by its own elastic reaction forced to snap into the hole 18g and thus be engaged therewith.
  • the hook 20b formed at the other end of the coil spring 20 is fastened to the pin 21 fixed to the cam driven gear 15d. This can be done either before or after the coil spring 20 is loosely fitted on the pivot shaft 18a.
  • the coil spring 20 continually exerts a specific torque on the release lever 18 urging it to rotate in its "closing" direction or clockwise as viewed in FIG. 3.
  • the anchor part 20a of the coil spring 20 is guided by the tapered part 18f of the pivot shaft 18a until the part 20a enters and engages with the hole 18g. Therefore there is no necessity of using special tools or jigs for assembly. Thus the assembly efficiency is high.
  • the decompression device of the above described construction according to the present invention operates in the following manner.
  • the flyweight 18c of the release lever 18 is in the "closed” state under the biasing force of the coil torsion spring 20.
  • the lift part 18d of the decompression cam 18b formed at the upper tip of the pivot shaft 18a coupled to the flyweight 8c is then projected out of the base circle of the exhaust cam 15e.
  • pivot shaft 18a rotates in the same direction as the flyweight 18c.
  • the lift part 18d thereby enters the base circle of the exhaust cam 15e.
  • the flyweight 18c pivots in the opening direction until it is arrested by the stop pin 19 as shown by single-dot chain line in FIG. 5.
  • the flat part 18e of the decompression cam 18b thereupon confronts the exhaust tappet 17.
  • This flat part 18e is on the inner side of the base circle of the exhaust cam 15e. For this reason, the exhaust tappet 17 is released from the lift-up state. Thus the decompression state is automatically terminated. The decompression device is then in the state indicated in FIG. 2.
  • the coil torsion spring 20 is biasing the flyweight 18c in the closing direction with a specific torque. Therefore there is no stretching as in the case of a conventional compression spring even during regular operation. Thus the stability is good at the time of inaction of the decompression device.
  • the intake tappet may be used for obtaining decompression operation.
  • Another possible modification is the use of both the exhaust tappet and the intake tappet for the decompression operation.
  • the present invention is not limited in application to a vertical-shaft engine.
  • it can be applied with equal effectiveness to other engine types such as the L-type, the V-type, and the horizontal type.
  • the present invention affords the features of merit and effectiveness enumerated below.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Valve Device For Special Equipments (AREA)
EP89118252A 1988-10-03 1989-10-02 Dispositif de décompression pour moteur à combustion interne Withdrawn EP0362775A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP130069/88 1988-10-03
JP13006988U JPH0250107U (fr) 1988-10-03 1988-10-03

Publications (1)

Publication Number Publication Date
EP0362775A1 true EP0362775A1 (fr) 1990-04-11

Family

ID=15025258

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89118252A Withdrawn EP0362775A1 (fr) 1988-10-03 1989-10-02 Dispositif de décompression pour moteur à combustion interne

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EP (1) EP0362775A1 (fr)
JP (1) JPH0250107U (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5197422A (en) * 1992-03-19 1993-03-30 Briggs & Stratton Corporation Compression release mechanism and method for assembling same
EP0555805A1 (fr) * 1992-02-10 1993-08-18 CAGIVA SERVICES S.p.A. Dispositif automatique de décompression pour le démarrage d'un moteur à combustion interne
CN1053482C (zh) * 1996-03-25 2000-06-14 光阳工业股份有限公司 使用于至少具有一动力汽缸的内燃机自动减压装置
US6269786B1 (en) * 1999-07-21 2001-08-07 Tecumseh Products Company Compression release mechanism
US6886518B2 (en) 2000-02-18 2005-05-03 Briggs & Stratton Corporation Retainer for release member
FR2883600A1 (fr) * 2005-03-23 2006-09-29 Simcoo Sarl Decompresseur a masselotte centrifuge

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1918844A1 (de) * 1968-04-18 1969-11-06 Tecumseh Products Co Verdichtungsverminderungsvorrichtung
EP0167691A2 (fr) * 1984-07-10 1986-01-15 Fuji Jukogyo Kabushiki Kaisha Dispositif de décompression pour moteur à combustion interne

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4835897A (fr) * 1971-09-08 1973-05-26

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1918844A1 (de) * 1968-04-18 1969-11-06 Tecumseh Products Co Verdichtungsverminderungsvorrichtung
EP0167691A2 (fr) * 1984-07-10 1986-01-15 Fuji Jukogyo Kabushiki Kaisha Dispositif de décompression pour moteur à combustion interne

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0555805A1 (fr) * 1992-02-10 1993-08-18 CAGIVA SERVICES S.p.A. Dispositif automatique de décompression pour le démarrage d'un moteur à combustion interne
US5197422A (en) * 1992-03-19 1993-03-30 Briggs & Stratton Corporation Compression release mechanism and method for assembling same
CN1053482C (zh) * 1996-03-25 2000-06-14 光阳工业股份有限公司 使用于至少具有一动力汽缸的内燃机自动减压装置
US6269786B1 (en) * 1999-07-21 2001-08-07 Tecumseh Products Company Compression release mechanism
US6886518B2 (en) 2000-02-18 2005-05-03 Briggs & Stratton Corporation Retainer for release member
FR2883600A1 (fr) * 2005-03-23 2006-09-29 Simcoo Sarl Decompresseur a masselotte centrifuge

Also Published As

Publication number Publication date
JPH0250107U (fr) 1990-04-09

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